Clonally distributed receptors on T lymphocytes provide the structural basis for selective antigen-specific regulatory and effector activities of these cells. To understand which receptors are expressed by the various T cell subsets showing distinctive antigen recognition spectra (eg class I restricted-CTL, class II restricted-helper cells, unrestricted-suppressor inducers), to determine the germ line repertoire from which these choices are made and the mechanisms controlling such choices throughout ontogeny, and to determine which structural features of these molecules account for their unique recognition and effector properties, it is necessary to clone representative members of this gene family. Such cloned genes can be sequenced, and also used as probes of germ line and expressed sets of receptor genes in different T cell subsets. Transfection of these cloned genes can be used as a tool to examine assembly of T cell receptor chains and to map the portions of the receptor involved in nominal antigen, restriction element, and alloantigen recognition. This approach can also establish whether so-called "T cell Ia" consists of epitopes on the receptor, and whether a modified form of the receptor constitutes a biologically active regulatory molecule (helper or suppressor factor). Towards these goals, the involvement of the recently identified T cell receptor gene locus in suppressor cell receptor formation has been examined.